It’s easy to overlook the philosophical, intellectual and theological storms that the merger between observational astronomy and theoretical physics precipitated.
It is possible to make an argument that there are only a handful of civilisations in the Milky Way galaxy today – perhaps we are the only one? – and this makes planet Earth a rare and valuable natural phenomenon. Value is in the eye of the beholder, and whilst it would be irrational to attach any universal significance to our temporary existence in a possibly infinite cosmos, I do not see any contradictions raised by the use of the word. Intelligence brings meaning to the Universe, albeit locally and temporarily. Our existence obviously means something to you and me, and I do not accept that our physical irrelevance and temporal transience devalues our lives one iota.
This is territory over which philosophy and theology still claim partial dominion, but science inevitably wanders into this intellectual no-man’s-land because to discuss the origin of life is to discuss the origin of humanity, with all the intellectual baggage that brings. Is it possible that my feelings, my morality, my hopes, fears and loves will be explained by some future biological Principia, as surely as the motions of the planets are explained by Newton? Is my apparent freedom of will an illusion resulting from the action of deterministic physical laws? Have those shadows on the wall of Plato’s cave deceived me into thinking I am special, as the rotating stars on the celestial sphere once conspired to? These are questions of a different emotional magnitude from those about our physical location in the Universe, and it is absolutely clear that they remain unsettled in the minds of many, although this is irrelevant in the sense that the veracity of a scientific theory is not decided by referendum.
These plates show Giovanni Aldini and colleagues in action, experimenting on both human cadavers and those of animals in an attempt to reanimate the corpses.
I think our modern understanding of biology and the scientific search for the origin of life must form an essential part of any serious philosophical debate about the meaning and value of human life. Having said that, given the overwhelming visceral force of our individual experience of living, it is perhaps not so paradoxical that the place of an individual human being in the Universe is still vigorously debated, whilst the physical position and significance of our planet is not.
The scientific quest to explain the origin of life became fashionable in spectacular style at the turn of the nineteenth century. Advances in surgery, pioneered by anatomists and surgeons such as John Hunter, dovetailed with the discoveries in electricity and magnetism pioneered by Faraday and his contemporaries, and coalesced into the search for a ‘vital principle’ – the animating force that separates living from inanimate matter. As far back as 1780, Luigi Galvani had been causing dead frogs’ legs to twitch ‘back into life’ by passing electrical currents through them, an approach that reached an infamous zenith in the hands of Giovanni Aldini, Galvani’s nephew, on 17 January 1803. Aldini procured the corpse of convicted murderer George Forster, fresh from the gallows at Newgate Prison, and attempted to reanimate it live on stage in front of an astonished audience. The Newgate Calendar reported it thus:
THIS IS THE DEEPEST VIEW OF OUR UNIVERSE EVER TAKEN. IT WAS ASSEMBLED FROM THOUSANDS OF IMAGES TAKEN BY THE HUBBLE SPACE TELESCOPE TO REVEAL A TINY PIECE OF SKY THAT WOULD BE COVERED BY A SMALL COIN HELD 20 METRES AWAY FROM THE OBSERVER. THERE ARE OVER TEN THOUSAND GALAXIES IN THE IMAGE.
I think our modern understanding of biology and the scientific search for the origin of life must form an essential part of any serious philosophical debate about the meaning and value of human life.
‘On the first application of the arcs to the face, the jaws of the deceased criminal began to quiver, and the adjoining muscles were horribly contorted, and the left eye was actually opened. The arms alternately rose and fell, the fists clenched and beat violently the table on which the body lay, natural respiration was artificially established…A lighted candle placed before the mouth was several times extinguished…Vitality might have been fully restored if many ulterior circumstances had not rendered this inappropriate.’
The growing fascination and disquiet surrounding the scientific push into such fraught territory was captured most famously in Mary Shelley’s novel Frankenstein; or, The Modern Prometheus. A writer knows they have done their job when reviews are polarised; it means they are operating in contested intellectual terrain. The poet and novelist Sir Walter Scott reviewed the novel favourably, although contemporary gossip had it that he may have been the author – Shelley had published the work anonymously. A critic writing for the Quarterly Review described it as ‘a tissue of horrible and disgusting absurdity’. I must remember that and aspire to write something worthy of such a label.
The junction between two cells, otherwise known as a synapse, can be seen in this colour-enhanced transmission electron microgram.
Today, Frankenstein’s ‘monster’ is a creature of B-movie horror films, but in Shelley’s novel the animated being is an articulate and moving voice.
‘And what was I? Of my creation and my creator I was absolutely ignorant? … No father had watched my infant days, no mother had blessed me with smiles and caresses …’
Two centuries later, with the whole of modern medical science, evolutionary biology and genetics to draw upon, we are still unable to reach an accommodation between our desire to discover a reason for our creation and the scientific consensus that no such reason exists beyond the inevitable action of the laws of nature on a young, active planet. The most interesting questions are those that demand a resolution between apparently irreconcilable positions.
On the Origin of Species
A framework to make sense of life on Earth
Forty years after the publication of Frankenstein, in November 1859, Charles Darwin’s On the Origin of Species provided the necessary conceptual framework for the scientific exploration of the origin of life, much as Einstein’s Theory of General Relativity provided the necessary conceptual framework for the study of the origin of the Universe. Darwin recognised that the great diversity of different species on Earth, the endless forms most beautiful, as he memorably called them, are related to one another. We now know this is correct, but for Darwin it was a radical proposal, indeed an act of genius, given the evidence available at the time. He was able to reach this conclusion by proposing a mechanism for new species to emerge from older ones: Evolution by natural selection.
Charles Darwin, who rocked Victorian society with the publication of his ideas on the origin of life.
There will be genetic variation in a population, which we now know to be caused by random mutations in the genetic code, the shuffling of genes by sex and a host of other mechanisms. Because organisms pass on genes to their offspring, combinations of genes that make an organism more likely to survive long enough to reproduce will become more common in a population. In this way, populations are shaped very rapidly by their interactions with the environment and with other living things. If populations become separated and have little or no interaction with each other, these processes drive them apart genetically, physically and behaviourally, and this is how new species emerge. Separation can be geographical, as in the case of the unique flora and fauna found on islands such as Madagascar, or it can result from different environmental niches opening up in a given location.
‘The intimate relation of Life with laws of chemical combination, & the universality of latter render spontaneous generation not improbable.’
– Charles Darwin
Once it is accepted that species do not appear fully formed, do not remain unchanged, and will inevitably evolve into new species if they are separated in time and space and exposed to different selection pressures, it is at least a possibility that all living things might have shared a common ancestor at some point in the past. As Darwin wrote: ‘Therefore I should infer from analogy that probably all organic beings which have ever lived on this earth have descended from some one
primordial form, into which life was first breathed’.
The title page of On the Origin of Species written by Charles Darwin’s own hand in 1859. The full text reads: ‘An Abstract of an Essay on the Origin of Species and Varieties through Natural Selection, by Charles Darwin, Fellow of the Royal, Geological, and Linnean Soc., London, 1859’.
Darwin didn’t know whether this was correct, but he knew it was possible. In a letter to his friend and colleague Joseph Hooker, he went further, speculating about the origin of life on Earth in some primordial ‘warm little pond’. It is said his imagination was fired after reading about an experiment demonstrating that some moulds could survive boiling.
‘It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured, or absorbed, which would not have been the case before living creatures were formed.’
It’s hard to overstate how bold and visionary Charles Darwin was. This was 1859, three years before Lord Kelvin declared that the Sun and therefore the Earth could be no more than 30 million years old, based on the known physics of the day. We will discuss the resolution to this problem in Chapter Four. It’s very difficult to imagine how some form of primitive single-celled organism could emerge from inanimate building blocks and then be transformed into a human being by the action of natural selection in a few million years. A few billion, on the other hand, is an entirely different matter. Darwin, quite rightly as it turned out, chose to ignore the physicists, and as the years progressed, evidence mounted for his idea of a warm little pond, a geological incubator within which ‘the first creature, the progenitor of innumerable extinct and living descendants, was created’.
The oldest life on Earth
If we are to build a scientific picture of Darwin’s warm little pond in the broadest sense, as the incubator for the first life on Earth, we need to understand what the conditions on our planet were like when life began. We also need to look for evidence of the earliest life, so we know how far back in time we have to go. This is non-trivial, to use a favourite phrase of physicists, because we can be sure that these events happened a long time ago.
Zircon, the oldest known material on Earth, at 4.4 billion years old, comes from a sedimentary gneiss in the Jack Hills of Australia’s Narryer Gneiss Terrane.
There is strong evidence that life existed 3.4 billion years ago from microfossils laid down in sandstone deposits at Marble Bar in Western Australia. The fossilised objects in the photographs certainly look like the remains of living cells, but visuals can be deceiving. Fortunately, it is possible to carry out a chemical analysis of these ancient structures, and signatures characteristic of a biological origin have been found. The concentrations of different isotopes of carbon in the structures can be used as a biomarker. Carbon has 6 protons in its atomic nucleus, and the most commonly occurring form also has 6 neutrons. This is known as the carbon-12 isotope. There is another naturally occurring form of carbon with 7 neutrons in the nucleus, known as carbon-13. Life prefers to use carbon-12, so therefore carbon deposits formed by biological processes are expected to show an excess of the lighter isotope. This is the case for the Marble Bar structures. There are also high concentrations of nitrogen in the proposed cell walls, again indicative of biological origin. Most biologists accept that these and other samples from different sites constitute strong evidence that single-celled organisms known as prokaryotes were abundant on Earth 3.4 billion years ago.
The oldest known objects on Earth were discovered in a remote region of Western Australia, north of the city of Perth, and remarkably they contain evidence of biology. Zircons are crystals found in igneous (volcanic) rocks. Despite being no bigger than a grain of sand and generally uninspiring to view, they are of immense scientific value because they are near-indestructible time capsules that carry their own internal clocks.
As the zircons form from cooling lava, tiny samples of atmospheric gases are sealed inside. Radioactive uranium atoms are also incorporated into the crystal structure, and using a highly accurate technique known as uranium-lead dating, the time since their formation can be measured to within a few million years. A sample from Erawandoo Hill, in the Jack Hills range, was recently dated at 4,404 +/- 8 million years old, making it the oldest object of terrestrial origin ever to be discovered. The Earth’s age is measured to be 4,540 +/- 50 million years old, so these crystals formed as the young Earth was cooling. Analysis of the trapped gases produced surprising results, challenging the commonly held picture of the young Earth as a Hadean hell of seething lava and toxic atmospheric gases. Earth was already a blue planet when some of the more ancient zircons formed, with liquid water on the surface. Atmospheric oxygen levels were low, which is unsurprising because photosynthesis is the primary source of atmospheric oxygen, but other than this, the primordial atmosphere appears to have been similar to that of today, with abundant nitrogen, carbon dioxide and water vapour as well as increased sulphur dioxide levels from the active volcanoes. This new evidence suggests that the very young Earth was a world of moderate temperatures, stable oceans and familiar air.
In November 2015, a team from UCLA and Stanford universities published a paper based on an analysis of over 10,000 zircons from the Jack Hills region, formed over 4.1 billion years ago.1 The zircons contained carbon deposits, and in common with the Marble Bar fossils, the ratio of carbon-12 to carbon-13 is suggestive of a biological origin. This is a surprising result; as team member Mark Harrison noted, the idea that life existed on Earth a billion years after its formation would have been near heretical only twenty years ago. If the interpretation of the new zircon results is correct, in Harrison’s words, ‘life may have started almost instantaneously’, and a terrestrial biosphere may have been well established 4.1 billion years ago.
The mounting evidence that life began on Earth pretty much as soon as it could lends a sense of inevitability to the emergence of biology from chemistry. This is, of course, a subjective judgement, because we have only a single planet as evidence, and firm conclusions are difficult to draw from sample sizes of one. This is another reason why the searches for life on Mars, or the moons of Jupiter or Saturn, or on exoplanets around nearby stars, are so important. We’ll have more to say about the study of planets beyond the Solar System in Chapter Four. That said, the observation that life may have emerged ‘almost instantaneously’ is an interesting one. Christian de Duve, the Belgian Nobel Prize-winning biochemist, argued that chemical reactions tend to proceed very quickly or not at all. Since biology is chemistry, then given the right conditions it follows that biology should happen very quickly or not at all, and the evidence from the zircons of Western Australia seems to point in this direction.
Despite being no bigger than a grain of sand, zircon crystals are of immense scientific value because they are near-indestructible time capsules that carry their own internal clocks.
The discovery of zircon crystals in the Jack Hills gives us evidence that the atmosphere 4.4. billion years ago was very similar to that of today.
British biologist Professor J B S Haldane, whose work demonstrated a genetic linkage in mammals and concluded that all life began in the ocean.
A warm little pond?
The idea that life might simply have ‘popped into existence’ from a soup of inanimate ingredients may seem either plausible or ridiculous to you. In the mid-nineteenth century, some of the great names in science were firmly on the side of ridiculous. The idea that life could arise from dead matter, known as spontaneous generation, had been discussed since the time of Aristotle. This is not unreasonable, because maggots appear to emerge fully formed from rotting meat. A series of experiments, most famously by Louis Pasteur a
nd, later, John Tyndall, appeared to refute this notion, and led to the so-called law of biogenesis; the idea that living things can be produced only from other living things. As Pasteur wrote of his experiment, rather immodestly, in 1864, ‘Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment’ and ‘those who think otherwise have been deluded by their poorly conducted experiments, full of errors they neither knew how to perceive, nor how to avoid.’
‘The link between living and dead matter is somewhere between a cell and an atom.’
– J B S Haldane, ‘The Origin of Life’, 1929
This is to confuse the spontaneous emergence of an intact, complex organism like a maggot or even a bacterium cell with the spontaneous emergence of life’s basic biochemistry – which is perhaps understandable if there is no known mechanism for complex living things to emerge from simpler forms. It is one of the many treasures of Darwin’s theory of evolution by natural selection that it describes such a mechanism, and as Darwin himself realised, this makes the spontaneous emergence of life at least a possibility; life can start simple. I don’t know why Pasteur didn’t notice that On the Origin of Species, which was published five years before he made his definitive statement, provides a way out. I leave that judgement to the historians; perhaps he hadn’t read it.
Forces of Nature Page 15
